Fun game
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Thought it looked like it could use a sunset because of the colours in the grass.
What I did:
Used a sunset off of one of my photos to add.
1. Copied just the clouds part of the photo and duplicated it (once for the sky, once for the water)
2. Flipped the water reflection upside down since that would mirror the sky.
3. Flipped the direction of the clouds because of the direction of the sunset here versus there (the sun would've been in the left side of my photo, but it's on the right here). Did that on the sky and water layers.
4. Masked the layers using "Select Color Range" and selected the sky and water.
5. Set both layers to "Multiply"
6. Refined the edges of the mask a little (though not 100% successfully in some of the areas by the trees)